The present invention is related to an improved solid electrolytic capacitor and a method of making a solid electrolytic capacitor. More specifically, the present invention is related to a capacitor design with improved volumetric efficiency and manufacturing robustness.
Solid electrolytic capacitors are well known in the art. Solid electrolytic capacitors comprise a solid porous anode with an anode lead wire extending there from. A dielectric and conductive layer, such as manganese dioxide or a conductive polymer, on the dielectric forms the cathode. An anode lead is electrically connected to the anode lead wire and a cathode lead is electrically connected to the cathode. The anode lead and cathode lead are typically formed by stamping a common metal strip which is referred to in the art as a lead frame wherein a lead frame may contain many connected anode and cathode leads stamped therein. The anode, with dielectric and cathode thereon, is placed in contact with the lead frame and the anode lead wire and cathode are electrically connected to the lead frame at the appropriate locations. Portions of the device are encased in a resin and the lead frame is cut to remove individual capacitors.
A particular problem is that portion of the anode lead which contacts the anode lead wire. Since it is highly preferable that the anode and cathode leads exit the finished capacitor in a common plane a step up region, such as a “U”-shaped portion of the anode portion of the lead frame is typically formed to fill the space between the plane of the lead frame and the anode lead wire. While satisfactory for most instances, as the size of capacitors decreases the strength of the step up region has now become a detriment to manufacturing efficiency. In particular, when the anode lead wire is welded to the step up of the anode lead the pressure of the welding apparatus can cause the step up to bend resulting in a distortion in the finished capacitor.
Efforts to relieve this problem have been presented as exemplified in U.S. Pat. No. 7,283,352. The step-up portion includes a downward projection, or auxiliary portion, which functions as a platform of support during welding. This technique, though helpful, limits the minimal separation between the edge of the capacitor and the anode body which is contrary to ongoing minimization efforts.
There has been an ongoing desire for an improved solid electrolytic capacitor and for an improved method of making an improved solid electrolytic capacitor.